Sanding of surfaces is usually carried out with one of two types of pieces of equipment. The simplest form of equipment is the so-called drum sander. This piece of equipment comprises a cylindrical drum, around which a strip of abrasive material is secured. A motor rotates the drum. The drum is moved around the work surface, (or the surface may be moved over the drum) and sands it smooth.
This type of equipment is reasonably economic to operate and is economical in its consumption of abrasive paper. However, the quality of surface finish is somewhat impaired. This is due to the gap at each end of the strip. It is also difficult to control since its area of contact between the paper and the surface is essentially a line contact, i.e. tangent to the drum.
Another form of equipment used is a so-called belt sander. In this type of equipment, a drum is provided, and adjacent the drum a tension roller is provided. The abrasive material consists of an endless belt of abrasive material. The belt is arranged around the drum and the tension roller. The drum is then rotated by a motor, thus causing the belt to abrade the work surface. This type of equipment produces a higher quality surface finish in use. However, even in this case the contact between the belt and the work surface is a line contact (i.e. a tangent to the drum) and this is difficult to control on some surfaces. Belt sanders are used frequently for the final or finish sanding of a hardwood floor surface, but have many other uses.
A disadvantage inherent in the use of both drum sanders and belt sanders is the fact that the point of contact between the sanding element, i.e. the sanding sheet or belt and the work surface, lies along a line contact defined by a tangent to the periphery of the main drum. Sanding is usually carried out because the surface to be sanded is initially uneven. It may, for example, define high spots and low spots. In addition, in the case of hardwood floors, for example, there are areas which are softer, where the grain is wider apart, and there are areas which are harder, where the grain is closer together.
In all these cases, the conventional drum sander or belt sander was liable to result in uneven surface finishes. In the hands of an inexperienced operator it could easily gouge the surface. Sanding of many products by drum or belt sanders had to carried out with great care and considerable skill and experience. In the past, for example, flooring installers and service person who use the sanders have usually been obliged to purchase both belt sanders and drum sanders. Both types of sanders provide only a line (or tangent) contact with the work surface. There are various disadvantages to this practice. In the first place, service persons such as the flooring installer must purchase two relatively expensive pieces of equipment. Secondly, the flooring installer or other service person must move both pieces of equipment from one job site to another, or alternatively, keep several sets of both types of equipment. When one piece of equipment becomes unservicable then it may be impossible to continue with the job even though the other piece of equipment is still in good condition. Thirdly there is the simple fact of cost to the flooring installer and also the fact that he must maintain a stock both of sheet sandpaper as well as sanding belts, so that each piece of equipment may be used as desired.
In the past, certain forms of belt sander have been available in which the belt was stretched between two rolls, along a more or less linear path. A work piece could be placed on the belt, and the belt would provide a sanding function over a rectangular area, where it contacted the belt.
However, these belt sanders which were commonly used in industrial and in wood working shops for sanding generally flat wood work pieces, themselves had certain disadvantages. In order to keep the belt central on the two rolls, the two rolls were formed with a somewhat convex profile, i.e. they were generally speaking of greater diameter in the centre and tapering down to a smaller diameter at each end. The purpose of this was to prevent the belt from wandering sideways across the rolls.
The end result of this process was that the effect of the belt sander tended to be somewhat uneven in that the belt was tighter in the centre than it was along the side. Consequently, the belt sander tended to sand in a somewhat uneven fashion.
It is desirable to provide a piece of equipment, which can be used for belt sanding with greater control of the surface contact. In this way, service persons such as flooring installers may buy one type only of equipment. There will then be substantial savings in operations, and service people will be able to provide their service in a more efficient and expeditious manner than with either type of sanding equipment described above, having only a line contact with the surface.